Spontaneous baroreflex indices do not correlate to carotid pulsatile elasticity

Pharmacologically derived baroreflex gain is correlated to carotid distensibility (Bonyhay et al., 1997), yet it is unknown if spontaneous baroreflex indices are also reflective of elasticity in the carotid barosensory area. We examined relations between three baroreflex gain measures and two carotid elasticity measures in 12 healthy, supine subjects (7 males, 5 females; 26-41 years). Baroreflex gains (beat-to-beat systolic pressure - RR interval relations) were determined from intravenous bolus nitroprusside followed by phenylephrine (modified Oxford technique), from pressure increases or decreases ≥ 3 beats during 20 min rest (spontaneous sequence analysis), and from low frequency (0.05-0.15 Hz) cross-spectral magnitude during 10 min of 0.25 Hz paced breathing (spontaneous spectral analysis). Pulsatile common carotid compliance and stiffness were derived from beat-by-beat pressure-diameter relations during 1 min of ultrasound B-mode image acquisition and concurrent Finapres arterial pressure measurement (38±6 beats). Oxford baroreflex gain ranged from 10.7 to 22.5, sequence gain ranged from 8.0 to 57.6, and spectral gain ranged from 3.9 to 29.8 msec/mmHg. Average carotid compliance ranged from 2.0 to 6.7 × 10^-7 m₂/kPa and stiffness ranged from 5.3 to 24.2 units. Oxford baroreflex gain was strongly related to both arterial compliance (r=0.71, P=0.009) and stiffness (r=-0.82, P=0.001). However, the two spontaneous baroreflex gain indices were not correlated to Oxford baroreflex gain nor to either measure of carotid elasticity (r<0.44, P>0.15). Thus, differences in carotid elasticity were not reflected in spontaneous baroreflex gain measures, and the vasoelastic component of the arterial baroreflex was related only to a pharmacologic gold standard measure.